Multilocus enzyme systems are a common and important feature of the human and mammalian genome. This research proposal is concerned with an in-depth multifaceted investigation of the biochemical genetics of the human alkaline phosphatases (ALPs) which represent a model example of such a system. At least three loci occur and they are differentially expressed in different tissues. Differences between the enzyme products of the several loci obtained from various human tissues (placenta, liver, kidney, bone and adult and fetal intestine) will be characterized in detail by inhibition studies using a series of aminoacid and peptide inhibitors; by electrophoresis; by thermostability studies; by crossreactivity studies using conventional antisera, and with monoclonal antibodies prepared by the mouse hybridoma technique, which will allow us to ask whether a particular antigenic determinant present on one ALP is present or absent on another. Similar studies will be carried out on ALPs from differnt tissues of other animal species. These investigations will enable us to analyze in detail the interrelationships of the several ALP loci both in man and other species, and identify the points in ALP evolution when gene duplications occurred. Other related investigations will include the search using monoclonal antibodies for ALP polymorhisms not detectable by electrophoresis; characterization of unusual ALPs in cell lines; and studies of the specific deficiency of liver/bone/kidney ALP in hypophosphatasia to determine whether cross-reacting but enzymically inactive protein is produced by the mutant allele, and whether there is genetic heterogeneity.